Supramolecular Switching Research Articles

Remote controlled supramolecular switching using a ring-substituted peri-naphthoindigo derivative

Guest-induced supramolecular switching in an organic solvent was done remotely by making change at an adjacent aqueous layer.

A generic method for fluorescence monitoring glycogen through patent blue V triggered supramolecular switching

Glycogen is one of the main biomacromolecules responsible for energy storage in almost all the organisms. Glycogen levels are a key indicator of health condition and also relevant to a number of diseases such as glycogenosis. So far, most of available glycogen detection approaches are sophisticated, indirect, time-consuming and frequently require pre-reaction to convert glycogen into glucose. In this report, we propose a novel probe called patent blue V (PBV) that can bind glycogen and turn on fluorescence in a precise manner. This probe works fairly well under different environments such as different pH, temperature or with various ions or in the presence of cell extracts. Importantly, PBV readily distinguishes glycogen from monosaccharides and a number of other saccharides. In addition the superb selectivity, the proposed glycogen detection method also shows an excellent sensitivity with a detection limit of 0.7 μM. Finally, the putative mechanism of the supramolecular interaction and fluorescence light-up of PBV was discussed taking advantage of a docking experiment.

Stimuli-Responsive Supramolecular Chirality Switching and Nanoassembly Constructed by n-Shaped Amphiphilic Molecules in Aqueous Solution.

Self-assembled nanomaterials composed of amphiphilic oligomers with functional groups have been applied in the fields of biomimetic chemistry and on-demand delivery systems. Herein, we report the assembly behavior and unique properties of an emergent n-shaped rod-coil molecule containing an azobenzene (AZO) group upon application of an external stimulus (thermal, UV light). The n-shaped amphiphilic molecules comprising an aromatic segment based on anthracene, phenyl linked with azobenzene groups, and hydrophilic oligoether (chiral) segments self-assemble into large strip-like sheets and perforated-nanocage fragments in an aqueous environment, depending on the flexible oligoether chains. Interestingly, the nano-objects formed in aqueous solution undergo a morphological transition from sheets and nanocages to small one-dimensional nanofibers. These molecules exhibit reversible photo- and thermal-responsiveness, accompanied by a change in the supramolecular chirality caused by the conformational transitions of the rod backbone. The architecture of n-shaped amphiphilic molecules with a photosensitive group makes them ideal candidates for intelligent materials for applications in advanced materials science.

Enhanced Electric Polarization and Polar Switching of Dipolar Aromatic Liquids Confined in Supramolecular Gel Networks.

Dipolar aromatic liquids confined in the interstitial domains of chiral organogels show significantly enhanced electric polarization, as compared with those of pure liquids alone or organogels formed with nonpolar liquids. Intriguingly, nitrobenzene gels showed a supramolecular polar switching phenomenon; i.e., hysteresis in the polarization (P)-electric field (E) curves was observed for the gel above the melting point of the solvent. This indicates that the nitrobenzene molecules confined in the chiral nanofibrous gel networks exert macroscopic polarization whose direction is inversed depending on the direction of the external electric field. The anomalously enhanced electric polarization and polar switching phenomenon of supramolecular gels in varied solvents are scrutinized by the positive-up-negative-down (PUND) measurements, and the interactions between the gel nanofibers and the polar solvent molecules play crucial roles for the emergence of the polar switching phenomenon. This work presents for the first time that dipolar liquid molecules filling the interstitial space of supramolecular gels exhibit a significant confinement effect. It provides a new perspective to design electric-field-responsive soft materials based on the functional liquid domains confined in their porous networks.

Cyclodextrin supramolecular inclusion-enhanced pyrene excimer switching for highly selective detection of RNase H

Here, we report a novel fluorescence method for the highly selective and sensitive detection of RNase H by combining the use of a dual-pyrene-labeled DNA/RNA duplex with supramolecular inclusion-enhanced fluorescence. Initially, the probe is in the “off” state due to the rigidness of the double-stranded duplex, which separates the two pyrene units. In the presence of RNase H, the RNA strand of the DNA/RNA duplex will be hydrolyzed, and the DNA strand transforms into a hairpin structure, bringing close the two pyrene units which in turn enter the hydrophobic cavity of a γ-cyclodextrin. As a result, the pyrene excimer emission is greatly enhanced, thereby realizing the detection of RNase H activity. Under optimal conditions, RNase H detection can be achieved in the range from 0.08 to 4 U/mL, with a detection limit of 0.02 U/mL.

Synergic Effect: Temperature-Assisted Electric-Field-Induced Supramolecular Phase Transitions at the Liquid/Solid Interface

Using trimesic acid (TMA) as a model system by means of scanning tunneling microscope (STM) equipped with a temperature controller, here, we report a temperature-assisted method to cooperatively control electric-field-induced supramolecular phase transitions at the liquid/solid interface. Octanoic acid is used as a solvent due to its good solubility for TMA and its less complicated pattern formed under negative STM bias (e.g., only chicken-wire polymorphs existing). At positive substrate bias, STM revealed that TMA assembly based on temperature modulations underwent phase transitions from a porous (22 °C) to a flower (45 °C) and further to a zigzag (68 °C) structure. The transitions are ascribed to the partial deprotonation of the carboxyl groups of TMA. Both the temperature and electrical polarity of the substrate are crucial, i.e., the transitions only take place at positive substrate bias and elevated temperatures. Molecular mechanics simulations were carried out to calculate the temperature and electric field dependence of the adsorption enthalpy and free energy of the chicken-wire assembly of TMA on the two layers of graphene surface. The calculated decrease in adsorption enthalpy with the increase of temperature and electric field values that causes the TMA chicken-wire assembly to be less stable is proposed to promote the occurrence of the phase transition observed by STM. This study paves the way toward program-controlled supramolecular phase switching via the synergic effect of electrical and thermal stimuli.

Supramolecular Switching Surface for Antifouling and Bactericidal Activities.

Antibacterial materials are often bothered by the problems of drug-resistance-induction and adhesion-to-invalidation, coming from the exposure of reusable bactericidal materials before or after utilization. Herein, an efficient and easily transformable supramolecular switching surface for antifouling and bactericidal was successfully fabricated, through introducing a negatively charged macrocyclic host S6-corona[3]arene[3]pyridazine (S6-CAP) to a contact-killing surface constructed by a positively charged amphiphilic bactericide. The S6-CAP was able to fully switch off the bactericidal activity and make the surfaces antifouling. After switched on by simply washing off much of S6-CAP, the bactericidal activity was even better than the original contact-killing surfaces.

Cucurbit[8]uril Reactivation of an Inactivated Caspase-8 Mutant Reveals Differentiated Enzymatic Substrate Processing.

Caspase‐8 constructs featuring an N‐terminal FGG sequence allow for selective twofold recognition by cucurbit[8]uril, which leads to an increase of the enzymatic activity in a cucurbit[8]uril dose‐dependent manner. This supramolecular switching has enabled for the first time the study of the same caspase‐8 in its two extreme states; as full monomer and as cucurbit[8]uril induced dimer. A mutated, fully monomeric caspase‐8 (D384A), which is enzymatically inactive towards its natural substrate caspase‐3, could be fully reactivated upon addition of cucurbit[8]uril. In its monomeric state caspase‐8 (D384A) still processes a small synthetic substrate, but not the natural caspase‐3 substrate, highlighting the close interplay between protein dimerization and active site rearrangement for substrate selectivity. The ability to switch the caspase‐8 activity by a supramolecular system thus provides a flexible approach to studying the activity of a protein at different oligomerization states.

Supramolecular chiroptical switching of helical-sense preferences through the two-way intramolecular transmission of a single chiral source.

We demonstrate a chiroptical switching system with a simple molecule. The molecule contains a pair of chromophores of diphenylacetylene that are linked with a diyne bond and arranged to exert exciton coupling in helically folded forms with (M)- or (P)-helicity. A tertiary amide group is attached to each end of the looped molecule. The amide carbonyls were used to capture a ditopic hydrogen-bonding guest. A chiral auxiliary group on the amide nitrogen acted as a chiral handle to control the helical-sense preference of dynamic helical forms of the loop. The helical-sense preference is brought about by an intramolecular transmission of point chirality associated with the loop. The preferred sense was switched upon complexation with an achiral additive through the formation of hydrogen bonds. In both states, before and after complexation, the helical-sense preferences were controlled through two-way transmission of the single chiral source.

A Ratiometric Luminescent Switch Based on Platinum Complexes Tethered to a Crown-Ether Scaffold.

A ratiometric chemosensor for potassium is reported, based on phosphorescent dinuclear cyclometalated Pt(II) complexes featuring a cis-crown ether as the cation-recognition unit. The metal complexes are blue luminescent in a non-aggregated state but become strongly orange emissive when in a close physical proximity, as is the case when the macrocycle is in the folded state. Upon binding of the cation, unfolding occurs, resulting in a pronounced change in the emission properties (e.g. emission wavelength), which can be used for ratiometric sensing applications. The reversibility of the binding was confirmed by competitive titration experiments with unsubstituted 18-crown-6; the system shows supramolecular switching behavior.

Engineering molecular self-assembly of perylene diimide through pH-responsive chiroptical switching

The perturbation of non-covalent interactions induced by pH-responsive protonation–deprotonation in HPH resulted in reversible supramolecular chiroptical switching (left-handed to right-handed helical self-assembly) and tunable 1D nanostructures.

Cyclodextrin supramolecular inclusion-enhanced pyrene excimer switching for time-resolved fluorescence detection of biothiols in serum

We report here an efficient pyrene excimer signaling-based time-resolved fluorescent sensor for the measurement of biothiols (cysteine (Cys), homocysteine (Hcy), glutathione (GSH)) in human serum based on thymine–Hg2+–thymine (T–Hg2+–T) coordination chemistry and the inclusion interaction of cyclodextrin. The sensing mechanism of the approach is based on the competitive ligation of Hg2+ ions by Hcy/Cys/GSH and T–T mismatches in a bis-pyrene-labeled DNA strand with the self-complementary 5′ and 3′ ends. The introduction of γ-cyclodextrin can provide cooperation for the molecular level space proximity of the two labeled pyrene molecules, moreover the hydrophobic cavity of γ-cyclodextrin can also offer protection for the pyrene dimer's emission from the quenching effect of environmental conditions and enhance the fluorescence intensity of the pyrene excimer. When the biothiols are not presented, the sensing ensemble is in the “off” state due to the long distance between the two labeled pyrene molecules resulted from the formation of a more stable T–Hg2+–T structure. While in the presence of biothiols, Hg2+ interacts very strongly with thiol groups and the T–Hg2+–T structure is dehybridized, and then the pyrene excimer will be formed due to the self-complementary 5′ and 3′ ends of the DNA probe and the cooperation interaction of γ-cyclodextrin to pyrene dimer, thus resulting in switching the sensing ensemble to the “on” state. In the optimum conditions described, the linear concentration range of 1.0–100μM with the limit of detection (LOD) of 0.36μM for GSH was obtained. Moreover, due to the much longer lifetime of the pyrene excimer fluorescence than those of the ubiquitous endogenous fluorescent components, the time-resolved fluorescence technique has been successfully used for application in complicated biological samples.

Supramolecular electron transfer-based switching involving pyrrolic macrocycles. A new approach to sensor development?

This Feature focuses on pyrrolic macrocycles that can serve as switches via energy- or electron transfer (ET) mechanisms. Macrocycles operating by both ground state (thermodynamic) and photoinduced ET pathways are reviewed and their ability to serve as the readout motif for molecular sensors is discussed. The aim of this article is to highlight the potential utility of ET in the design of systems that perform molecular switching or logic functions and their applicability in chemical sensor development. The conceptual benefits of this paradigm are illustrated with examples drawn mostly from the authors' laboratories.

Assembly modulation of PDI derivative as a supramolecular fluorescence switching probe for detection of cationic surfactant and metal ions in aqueous media.

We report an amphiphilic perylene diimide (1), a bimolecular analog of l-3,4-dihydroxyphenylalanine (L-DOPA), as a reversible fluorescence switching probe for the detection and sensing of cationic surfactants and Fe(3+)/Cu(2+) in an aqueous media respectively by means of host-guest interactions driven assembly and disassembly of 1. Photophysical studies of 1, going from dimethyl sulfoxide (DMSO) (State-I) to pure aqueous medium (State-II), suggested the formation of self-assembled aggregates by displaying very weak fluorescence emission along with red shifted broad absorption bands. Interestingly, the cationic surfactant cetyltrimethylammonium bromide (CTAB) could disassemble 1 in miceller conditions by restoring bright yellow fluorescence and vibronically well-defined (Franck-Condon progressions A0-0/A0-1 ≈ 1.6) absorption bands of 1 over other neutral and anionic surfactants (State-III). Owing to the metal chelating nature of L-DOPA, 1 was able to sense Fe(3+) and Cu(2+) among a pool of other metal ions by means of fluorescence switching off state, attributed to metal interaction driven assembly of 1 (State-IV). Such metallosupramolecular assemblies were found to reverse back to the fluorescence switching on state using a metal ion chelator, diethylenetriaminepentaacetic acid (DTPA, State-III), further signifying the role of metal ions toward assembly of 1. Formation of assembly and disassembly could be visualized by the diminished and increased yellow emission under green laser light. Further, the assembly-disassembly modulation of 1 has been extensively characterized using infrared (IR), mass spectrometry, microscopy and dynamic light scattering (DLS) techniques. Therefore, modulation of the molecular self-assembly of PDI derivative 1 in aqueous media (assembled state, State-II) by means of host-guest interactions provided by micellar structures of CTAB (disassembled state, State-III), metal ion (Fe(3+) and Cu(2+)) interactions (assembled state, State-IV) and metal ion sequestration using DTPA (disassembled state, State-III) is viewed as a supramolecular reversible fluorescence switching off-on probe for cationic surfactant CTAB and Fe(3+)/Cu(2+).

Supramolecular Switching between Flat Sheets and Helical Tubules Triggered by Coordination Interaction

Here we report the spontaneous formation of switchable sheets in aqueous solution, which is based on bent-shaped aromatic amphiphiles containing m-pyridine units at the terminals and a hydrophilic dendron at the apex. The aromatic segments self-assemble into flat sheets consisting of a zigzag conformation through π-π stacking interactions. Notably, the sheets reversibly transform into helical tubules at higher concentration and into discrete dimeric macrocycles at a lower concentration in response to Ag(I) ions through reversible coordination interactions between the pyridine units of the aromatic segments and the Ag(I) ions. While maintaining the coordination bonding interactions, the helical tubules reversibly transform into the dimeric macrocycles in response to the variation in concentration.

Inside Cover: Hydrogen-Bonding Induced Alternate Stacking of Donor (D) and Acceptor (A) Chromophores and their Supramolecular Switching to Segregated States (Chem. Eur. J. 32/2012)

Inside Cover: Hydrogen-Bonding Induced Alternate Stacking of Donor (D) and Acceptor (A) Chromophores and their Supramolecular Switching to Segregated States (Chem. Eur. J. 32/2012)

Hydrogen‐Bonding Induced Alternate Stacking of Donor (D) and Acceptor (A) Chromophores and their Supramolecular Switching to Segregated States

This paper reports comprehensive studies on the mixed assembly of bis-(trialkoxybenzamide)-functionalized dialkoxynaphthalene (DAN) donors and naphthalene-diimide (NDI) acceptors due the cooperative effects of hydrogen bonding, charge-transfer (CT) interactions, and solvophobic effects. A series of DAN as well as NDI building blocks have been examined (wherein the relative distance between the two amide groups in a particular chromophore is the variable structural parameter) to understand the structure-dependent variation in mode of supramolecular assembly and morphology (organogel, reverse vesicle, etc.) of the self-assembled material. Interestingly, it was observed that when the amide functionalities are introduced to enhance the self-assembly propensity, the mode of co-assembly among the DAN and NDI chromophores no longer remained trivial and was dictated by a relatively stronger hydrogen-bonding interaction instead of a weak CT interaction. Consequently, in a highly non-polar solvent like methylcyclohexane (MCH), although kinetically controlled CT-gelation was initially noticed, within a few hours the system sacrificed the CT-interaction and switched over to the more stable self-sorted gel to maximize the gain in enthalpy from the hydrogen-bonding interaction. In contrast, in a relatively less non-polar solvent such as tetrachloroethylene (TCE), in which the strength of hydrogen bonding is inherently weak, the contribution of the CT interaction also had to be accounted for along with hydrogen bonding leading to a stable CT-state in the gel or solution phase. The stability and morphology of the CT complex and rate of supramolecular switching (from CT to segregated state) were found to be greatly influenced by subtle structural variation of the building blocks, solvent polarity, and the DAN/NDI ratio. For example, in a given D-A pair, by introducing just one methylene unit in the spacer segment of either of the building blocks a complete change in the mode of co-assembly (CT state or segregated state) and the morphology (1D fiber to 2D reverse vesicle) was observed. The role of solvent polarity, structural variation, and D/A ratio on the nature of co-assembly, morphology, and the unprecedented supramolecular-switching phenomenon have been studied by detail spectroscopic and microscopic experiments in a gel as well as in the solution state and are well supported by DFT calculations.

Hg2+-Selective OFF−ON and Cu2+-Selective ON−OFF Type Fluoroionophore Based upon Cyclam

[structure: see text]. A new cyclam derivative having two different fluorophores of pyrene and NBD subunits was prepared, and its Hg2+- and Cu2+-selective signaling behaviors were investigated. The detection limits for the analysis of Hg2+ and Cu2+ ions were found to be 7.9 x 10(-6) and 2.6 x 10(-7) M in aqueous acetonitrile solution (H2O-CH3CN = 10:90, v/v), respectively. The compound also exhibited a selective Hg2+/Cu2+-induced OFF-ON-OFF type of signaling pattern that can be utilized for the construction of functional supramolecular switching systems.

Dynamic devices. Shape switching and substrate binding in ion-controlled nanomechanical molecular tweezers.

As examples of supramolecular devices performing chemical (ionic, molecular) control of binding events and models of related natural systems, two molecular conformational switches are described, which display cation-controlled nanomechanical motion coupled to substrate binding and release. The substrate binding relies on donor/acceptor interactions, provided by intercalation between planar sites located at the extremities of the switching units, whereas cation complexation is responsible for conformational regulation. The terpyridine py-py-py-based receptor is activated toward substrate binding upon complexation of a zinc(II) cation and operates in a two-state process. The replacement of the central pyridine by a 4,6-disubstituted pyridimine as in py-pym-py induces a state reversal and yields a new receptor which binds a substrate in the absence of cation, and releases it when copper(I) is introduced, following a three-step process. These systems represent effector-triggered supramolecular switching devices leading toward multistate nanomechanical chemical systems. These two systems illustrate the use of simple conformational switches in the binding site and allosteric regulation of substrate affinity.